Certain aromatization process for preparing 1-alkyl-1,4-dihydro-4-oxo-7-(4-pyridyl)-3-quinoline carboxylic acid

Abstract

A 4-cyclohexenylpyridine is brominatively aromatized to the corresponding 4-phenylpyridine by brominating the cyclohexenylpyridine, such as a 4-(halocyclohexenyl)pyridine, especially a 4-(4-halocyclohex-3-enyl)pyridine hydrochloride, and heating the brominated product in the presence or absence of any added base or hydrogen acceptor to form, e.g., a 4-(halophenyl)pyridine. The invention is of particular utility in the manufacture of intermediates of antibacterial 1-alkyl-1,4-dihydro-4-oxo-7-(4-pyridyl)-3-quinolinearcarboxylic acids.

We claim: 
     
       1. In a process for preparing a 1-alkyl-1,4-dihydro-4-oxo-7-(4-pyridyl)-3-quinolinecarboxylic acid by (a) reacting a haloprene with a 4-vinylpyridine to form a 4-(4-halocyclohex-3-enyl)pyridine, (b) reacting the 4-(4-halocyclohex-3-enyl)pyridine with hydrochloric acid to form a hydrochloride, (c) aromatizing the resultant 4-(4-halocyclohex-3-enyl)pyridine hydrochloride to a 4-(4-halophenyl)pyridine, (d) nitrating the 4-(4-halophenyl)pyridine, (e) reducing the resultant 4-(4-halo-3-nitrophenyl)pyridine to a 4-(3-aminophenyl)pyridine, (f) converting the 4-(3-aminophenyl)pyridine to an alkyl 1-alkyl-1,4-dihydro-4-oxo-7-(4-pyridyl)-3-quinolinecarboxylate, and (g) hydrolyzing the resultant ester, the improvement which comprises aromatizing the 4-(4-halocyclohex-3-enyl)pyridine hydrochloride by reacting it with 1-5 molar equivalents of a brominating agent at a temperature of 20°-70° C. to add bromine to the double bond of the cyclohexene ring and heating the resultant brominated product at a temperature of 80°-300°  C. to form the 4-(4-halophenyl)pyridine.